Permeable cement and sand control methods utilizing permeable cement in subterranean well bores

ABSTRACT

Cement compositions useful in subterranean applications are provided. More particularly, permeable cement compositions for forming consolidated permeable cement masses in well bores to prevent sand influx into the well bores with produced fluids are provided. In one embodiment, the permeable cement compositions of the present invention comprise a hydraulic cement, water, and a degradable material capable of undergoing an irreversible degradation downhole selected from the group consisting of a degradable polymer selected from the group consisting of polysaccharides, chitins, chitosans, proteins, aliphatic polyesters, poly(lactides), poly(glycolides), poly(ε-caprolactones), poly(hydroxybutyrates), polyanhydrides, aliphatic polycarbonates, poly(orthoesters), poly(amino acids), poly(ethylene oxides), and polyphosphazenes; and a dehydrated salt.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 10/608,319 entitled “Permeable Cement and Sand Control MethodsUtilizing Permeable Cement in Subterranean Well Bores,” filed on Jun.27, 2003, the entire disclosure of which is incorporate herein byreference.

BACKGROUND

This invention relates to improved methods for completing wells inunconsolidated subterranean zones. More specifically, the presentinvention relates to cement compositions useful in subterraneanapplications, and more particularly, to permeable cement compositionsand methods for forming consolidated permeable cement masses in wellbores to prevent sand influx into the well bores with produced fluids.

Oil, gas, and water producing wells often are completed inunconsolidated subterranean formations containing loose or incompetentsand that flows into the well bores with produced fluids. The presenceof this sand in the produced fluids is undesirable as it, inter alia,may erode equipment, which often substantially increases the costsassociated with operating such wells and generally reduces the fluidproduction capability of the formation. Incompetent subterraneanformations include those which contain loose sand that is readilyentrained by produced fluids, and those wherein the bonded sandparticles comprising the formations lack sufficient bond strength towithstand the forces produced by the intermittent production of fluidsfrom the formations.

Heretofore, unconsolidated formations have been treated by creatingfractures in the formations and depositing proppant material, e.g., sandof a selected size, in the fractures to substantially preserve thefractures. In addition, the proppant has heretofore been consolidatedwithin the fractures into hard permeable masses to prevent the proppantfrom flowing back and to reduce the migration of sand through thefractures with produced fluids. Further, costly “gravel packs,” whichmay include sand screens, slotted liners, and the like, have beenutilized in wells to prevent the production of formation sand. In gravelpacking operations, e.g., graded sand, is placed in the annulus betweena screen and the walls of the well bore in the producing interval. Theresulting structure provides a barrier to migrating sand while allowingdesired fluids to flow into the well bore so that they may be produced.

While gravel packs may prevent the production of sand with formationfluids, they often fail and require replacement. This may be due to, forexample, the deterioration of the screen as a result of corrosion or thelike. The initial installation of a gravel pack adds considerableexpense to the cost of completing a well, and the removal andreplacement of a failed gravel pack is even more costly.

In horizontal well bores formed in unconsolidated formations, the wellbores are often completed open hole, e.g., a casing is not inserted intothe well bore. In open hole well bores, oftentimes a slotted liner, sandcontrol screen, gravel pack, or the like is installed into the uncasedwell bore. This method of completion may be problematic as discussedabove in that as the incompetent formation tends to break down as aresult of production, the slotted liner, sand control screen, or gravelpack is often bypassed, which may result in formation sand beingproduced along with formation fluids.

There have been attempts to use a sort of permeable cement in subsurfaceapplications such as gravel packs wherein the permeable cementcomposition contains a particulate, such as a carbonate salt oroil-soluble resin particulate, that is dissolvable with the addition ofa second fluid, e.g., an acid or a hydrocarbon. The thought behind thisapproach is generally that when the dissolvable particulate dissolvesout of the cement mass, voids are left in the cement mass so that thecement mass has some degree of permeability to formation fluids. Suchpermeable cement compositions and methods, however, have not beensuccessful because the permeability of the cement mass once theparticulate is dissolved out has not been satisfactory. This lack ofpermeability is caused by, inter alia, the dissolvable particulate'sdependence on contact with a second solvent. Oftentimes, the solvent isnot able to interact with a sufficient amount of the dissolvableparticulate to adequately dissolve a sufficient amount of theparticulate. As a result, not enough of the particulate is dissolved outof the cement mass to make the cement mass's permeability suitable forsubsurface applications such as gravel packing.

SUMMARY

This invention relates to improved methods for completing wells inunconsolidated subterranean zones. More specifically, the presentinvention relates to cement compositions useful in subterraneanapplications, and more particularly, to permeable cement compositionsand methods for forming consolidated permeable cement masses in wellbores to prevent sand influx into the well bores with produced fluids.

In one embodiment, the present invention provides a permeable cementcomposition for use in subterranean operations comprising a hydrauliccement, water, and a degradable material selected from the groupconsisting of: (i) a degradable polymer selected from the groupconsisting of polysaccharides, chitins, chitosans, proteins, aliphaticpolyesters, poly(lactides), poly(glycolides), poly(ε-caprolactones),poly(hydroxybutyrates), polyanhydrides, aliphatic polycarbonates,poly(orthoesters), poly(amino acids), poly(ethylene oxides), andpolyphosphazenes; and (ii) a dehydrated salt.

In another embodiment, the present invention provides a permeable cementmass useful in well bores penetrating a subterranean formation as a sandcontrol means having voids created by a degradation of a degradablematerial selected from the group consisting of: (i) a degradable polymerselected from the group consisting of polysaccharides, chitins,chitosans, proteins, aliphatic polyesters, poly(lactides),poly(glycolides), poly(ε-caprolactones), poly(hydroxybutyrates),polyanhydrides, aliphatic polycarbonates, poly(orthoesters), poly(aminoacids), poly(ethylene oxides), and polyphosphazenes; and (ii) adehydrated salt.

The objects, features and advantages of the present invention will bereadily apparent to those skilled in the art upon a reading of thedescription of the preferred embodiments which follows.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides improved methods of preventing theproduction of sand with fluids produced from subterranean formations.The methods presented herein may be utilized in either vertical,deviated, or horizontal well bores that are open-hole, and/orunderreamed, or have casing cemented therein. If the method is carriedout in a cased wellbore, in certain embodiments the casing may beperforated to allow for fluid communication between the well bore andthe surrounding subterranean zone.

In accordance with the present invention, a permeable cement mass isformed in a well bore adjacent to a producing interval or zone wherebyloose or incompetent sands, inter alia, are prevented from entering thewell bore with fluids produced from the interval or zone. The permeablecement compositions of the present invention can be used in conjunctionwith sand control screens if desired. The term “screen” as used hereinrefers generically to any and all types of permeable structures commonlyused in gravel pack operations that permit flow of fluids therethroughwhile blocking the flow of particulates (e.g., commercially-availablescreens, slotted or perforated liners or pipes, screened pipes,prepacked screens, expandable-type screens and/or liners, or anycombination thereof). After the consolidated permeable cement mass hasformed in the well bore, the well is produced and the consolidatedpermeable cement mass functions as, inter alia, a sand screen. That is,produced liquids and gases flow through the permeable cement mass intothe well bore, but formation sands in the formation are prevented fromentering the well bore. Thus, the cement is permeable to desirablefluids yet impermeable to undesirable particulates.

The permeable cement compositions of the present invention comprise ahydraulic cement, water, and a degradable material that is capable ofundergoing an irreversible degradation downhole. The term “irreversible”as used herein means that the degradable material once degradeddownhole, should not recrystallize or reconsolidate while downhole,e.g., the degradable material should degrade in situ but notrecrystallize or reconsolidate in situ. The terms “degradation,”“degradable”, and the like when used herein refer to both the tworelatively extreme cases of hydrolytic degradation that the degradablematerial may undergo, i.e., heterogeneous (or bulk erosion) andhomogeneous (or surface erosion), and any stage of degradation inbetween these two. This degradation may be a result of, inter alia, achemical or thermal reaction or a reaction induced by radiation.

A variety of hydraulic cements are suitable in the compositions andmethods of the present invention including those comprised of calcium,aluminum, silicon, oxygen, and/or sulfur, which set and harden byreaction with water. Such hydraulic cements include, but are not limitedto, Portland cements, pozzolana cements, gypsum cements, high aluminacontent cements, silica cements, and high alkalinity cements. Portlandcements are generally preferred. In some embodiments, the Portlandcements that are suited for use in conjunction with the presentinvention are classified as Class A, B, C, G, and H cements according toAmerican Petroleum Institute, API Specification for Materials andTesting for Well Cements, API Specification 10, Fifth Ed., Jul. 1, 1990.Another useful cement for certain embodiments of the present inventioninclude a cement that is commercial available under the tradename“THERMALOCK™” from Halliburton Energy Services, Inc., in Duncan, Okla.,and described in U.S. Pat. No. 6,488,763, herein incorporated byreference.

Low-density cements are also suitable for use in the compositions andmethods of the present invention. Such low-density cements may be foamedcements or may be cements whose density has been reduced by anothermeans including microspheres, low-density polymer beads, or otherdensity-reducing additives. If a low-density cement is utilized, then amixture of foaming and foam stabilizing dispersants may be used.Generally, the mixture may be included in the cement compositions of thepresent invention in an amount in the range of from about 1% to about 5%by volume of water in the composition. Using a low-density cement in themethods of the present invention may help minimize the potential offracturing the walls of the well bore during placement of the cement inthe annulus.

The cement component of the compositions of the present inventioncomprises about 30% to about 70% of the weight of the composition,preferably from about 50% to about 60%.

The water utilized in the cement compositions of this invention can befresh water, salt water (e.g., water containing one or more saltsdissolved therein), brine (e.g., saturated salt water), or seawater.Generally, the water can be from any source provided that it does notcontain an excess of compounds that adversely affect other components inthe permeable cement composition. The water preferably is present in anamount sufficient to form a pumpable slurry. More particularly, thewater is present in the cement compositions in an amount in the range offrom about 15% to about 40% by weight of hydraulic cement therein, morepreferably in an amount of about 20% to about 35%.

Optionally, a dispersant may be included in the permeable cementcompositions of the present invention. If used, the dispersant should beincluded in the composition in an amount effective, inter alia, to aidin dispersing the cement and the degradable material within thecomposition. In certain embodiments, about 0.1% to about 5% dispersantby weight of the composition is suitable. In other embodiments, adifferent range may be suitable. Examples of suitable dispersantsinclude but are not limited to naphthalene sulfonate formaldehydecondensates, acetone formaldehyde sulfite condensates, and glucan deltalactone derivatives. Those skilled in the art with the benefit of thisdisclosure will recognize that other dispersants may be suitable for agiven application.

In order to prevent fluid loss from a permeable cement composition ofthis invention during placement, a fluid loss additive can be includedin the composition. Examples of suitable cement slurry fluid losscontrol additives include those that are liquids or can be dissolved orsuspended in liquids. These include but are not limited to modifiedsynthetic polymers and copolymers, natural gums and their derivatives,derivatized cellulose, and starches. Those skilled in the art with thebenefit of this disclosure will recognize that other fluid loss controladditives may be suitable for a given application. In some embodimentsof the present invention, the fluid loss additive may be present in anamount ranging from about 0% to about 25% by weight of the permeablecement composition.

Other additives such as accelerators (such as triethanolamines, calciumchloride, potassium chloride, sodium formate, sodium nitrate, and otheralkali and alkaline earth metal halides, formates, nitrates, andcarbonates), retardants (such as sodium tartrate, sodium citrate, sodiumgluconate, sodium itaconate, tartaric acid, citric acid, gluconic acid,lignosulfonates, and synthetic polymers and copolymers), weightingagents, thixotropic additives, suspending agents, or the like may alsobe included in the permeable cement compositions.

Nonlimiting examples of degradable materials that may be used inconjunction with the present invention include but are not limited todegradable polymers, dehydrated salts, and/or mixtures of the two.

As for degradable polymers, a polymer is considered to be “degradable”herein if the degradation is due to, inter alia, chemical and/or radicalprocess such as hydrolysis, oxidation, or UV radiation. Thedegradability of a polymer depends at least in part on its backbonestructure. For instance, the presence of hydrolyzable and/or oxidizablelinkages in the backbone often yields a material that will degrade asdescribed herein. The rates at which such polymers degrade are dependenton factors such as the type of repetitive unit, composition, sequence,length, molecular geometry, molecular weight, morphology (e.g.,crystallinity, size of spherulites, and orientation), hydrophilicity,hydrophobicity, surface area, and additives. Also, the environment towhich the polymer is subjected may affect how it degrades, e.g.,temperature, presence of moisture, oxygen, microorganisms, enzymes, pH,and the like.

Suitable examples of degradable polymers that may be used in accordancewith the present invention include but are not limited to thosedescribed in the publication of Advances in Polymer Science, Vol. 157entitled “Degradable Aliphatic Polyesters” edited by A.-C. Albertsson.Specific examples include homopolymers, random, block, graft, and star-and hyper-branched aliphatic polyesters. Polycondensation reactions,ring-opening polymerizations, free radical polymerizations, anionicpolymerizations, carbocationic polymerizations, coordinativering-opening polymerizations, and any other suitable process may preparesuch suitable polymers. Specific examples of suitable polymers includepolysaccharides such as dextran or cellulose; chitin; chitosan;proteins; aliphatic polyesters; poly(lactide); poly(glycolide);poly(ε-caprolactone); poly(hydroxybutyrate); poly(anhydrides); aliphaticpolycarbonates; poly(orthoesters); poly(amino acids); poly(ethyleneoxide); and polyphosphazenes. Of these suitable polymers, aliphaticpolyesters and polyanhydrides are preferred.

Aliphatic polyesters degrade chemically, inter alia, by hydrolyticcleavage. Hydrolysis can be catalyzed by either acids or bases.Generally, during the hydrolysis, carboxylic end groups are formedduring chain scission, and this may enhance the rate of furtherhydrolysis. This mechanism is known in the art as “autocatalysis,” andis thought to make polyester matrices more bulk eroding.

Suitable aliphatic polyesters have the general formula of repeatingunits shown below:

where n is an integer between 75 and 10,000 and R is selected from thegroup consisting of hydrogen, alkyl, aryl, alkylaryl, acetyl,heteroatoms, and mixtures thereof. Of the suitable aliphatic polyesters,poly(lactide) is preferred. Poly(lactide) is synthesized either fromlactic acid by a condensation reaction or more commonly by ring-openingpolymerization of cyclic lactide monomer. Since both lactic acid andlactide can achieve the same repeating unit, the general termpoly(lactic acid) as used herein refers to Formula I without anylimitation as to how the polymer was made such as from lactides, lacticacid, or oligomers, and without reference to the degree ofpolymerization or level of plasticization.

The lactide monomer exists generally in three different forms: twostereoisomers 1- and d-lactide and racemic D,L-lactide (meso-lactide).The oligomers of lactic acid, and oligomers of lactide are defined bythe formula:

where m is an integer: 2≦m≦75. Preferably m is an integer: 2≦m≦10. Theselimits correspond to number average molecular weights below about 5,400and below about 720, respectively. The chirality of the lactide unitsprovides a means to adjust, inter alia, degradation rates, as well asphysical and mechanical properties. Poly(L-lactide), for instance, is asemicrystalline polymer with a relatively slow hydrolysis rate. Thiscould be desirable in applications of the present invention where aslower degradation of the degradable particulate is desired.Poly(D,L-lactide) may be a more amorphous polymer with a resultantfaster hydrolysis rate. This may be suitable for other applicationswhere a more rapid degradation may be appropriate. The stereoisomers oflactic acid may be used individually or combined to be used inaccordance with the present invention. Additionally, they may becopolymerized with, for example, glycolide or other monomers likeε-caprolactone, 1,5-dioxepan-2-one, trimethylene carbonate, or othersuitable monomers to obtain polymers with different properties ordegradation times. Additionally, the lactic acid stereoisomers can bemodified to be used in the present invention by, inter alia, blending,copolymerizing or otherwise mixing the stereoisomers, blending,copolymerizing or otherwise mixing high and low molecular weightpolylactides, or by blending, copolymerizing or otherwise mixing apolylactide with another polyester or polyesters.

Plasticizers may be present in the polymeric degradable materials of thepresent invention. The plasticizers may be present in an amountsufficient to provide the desired characteristics, for example, (a) moreeffective compatibilization of the melt blend components, (b) improvedprocessing characteristics during the blending and processing steps, and(c) control and regulation of the sensitivity and degradation of thepolymer by moisture. Suitable plasticizers include but are not limitedto derivatives of oligomeric lactic acid, selected from the groupdefined by the formula:

where R is a hydrogen, alkyl, aryl, alkylaryl, acetyl, heteroatom, or amixture thereof and R is saturated, where R′ is a hydrogen, alkyl, aryl,alkylaryl, acetyl, heteroatom, or a mixture thereof and R′ is saturated,where R and R′ cannot both be hydrogen, where q is an integer: 2≦q≦75;and mixtures thereof. Preferably q is an integer: 2≦q≦10. As used hereinthe term “derivatives of oligomeric lactic acid” includes derivatives ofoligomeric lactide. In addition to the other qualities above, theplasticizers may enhance the degradation rate of the degradablepolymeric materials. The plasticizers, if used, are preferably at leastintimately incorporated within the degradable polymeric materials.

Aliphatic polyesters useful in the present invention may be prepared bysubstantially any of the conventionally known manufacturing methods suchas those described in U.S. Pat. Nos. 6,323,307; 5,216,050; 4,387,769;3,912,692; and 2,703,316, the relevant disclosure of which areincorporated herein by reference.

Polyanhydrides are another type of particularly suitable degradablepolymer useful in the present invention. Polyanhydride hydrolysisproceeds, inter alia, via free carboxylic acid chain-ends to yieldcarboxylic acids as final degradation products. The erosion time can bevaried over a broad range of changes in the polymer backbone. Examplesof suitable polyanhydrides include poly(adipic anhydride), poly(subericanhydride), poly(sebacic anhydride), and poly(dodecanedioic anhydride).Other suitable examples include but are not limited to poly(maleicanhydride) and poly(benzoic anhydride).

The physical properties of degradable polymers depend on several factorssuch as the composition of the repeat units, flexibility of the chain,presence of polar groups, molecular mass, degree of branching,crystallinity, orientation, etc. For example, short chain branchesreduce the degree of crystallinity of polymers while long chain brancheslower the melt viscosity and impart, inter alia, elongational viscositywith tension-stiffening behavior. The properties of the materialutilized can be further tailored by blending, and copolymerizing it withanother polymer, or by a change in the macromolecular architecture(e.g., hyper-branched polymers, star-shaped, or dendrimers, etc.). Theproperties of any such suitable degradable polymers (e.g.,hydrophobicity, hydrophilicity, rate of degradation, etc.) can betailored by introducing select functional groups along the polymerchains. For example, poly(phenyllactide) will degrade at about ⅕th ofthe rate of racemic poly(lactide) at a pH of 7.4 at 55° C. One ofordinary skill in the art with the benefit of this disclosure will beable to determine the appropriate functional groups to introduce to thepolymer chains to achieve the desired physical properties of thedegradable polymers.

Dehydrated salts may be used in accordance with the present invention asa degradable material. A dehydrated salt is suitable for use in thepresent invention if it will degrade over time as it hydrates. Forexample, a particulate solid anhydrous borate material that degradesover time may be suitable. Specific examples of particulate solidanhydrous borate materials that may be used include but are not limitedto anhydrous sodium tetraborate (also known as anhydrous borax), andanhydrous boric acid. These anhydrous borate materials are only slightlysoluble in water. However, with time and heat in a subterraneanenvironment, the anhydrous borate materials react with the surroundingaqueous fluid and are hydrated. The resulting hydrated borate materialsare highly soluble in water as compared to anhydrous borate materialsand as a result degrade in the aqueous fluid. In some instances, thetotal time required for the anhydrous borate materials to degrade in anaqueous fluid is in the range of from about 8 hours to about 72 hoursdepending upon the temperature of the subterranean zone in which theyare placed. Other examples include organic or inorganic salts likeacetate trihydrate.

Blends of certain degradable materials may also be suitable. One exampleof a suitable blend of materials is a mixture of poly(lactic acid) andsodium borate where the mixing of an acid and base could result in aneutral solution where this is desirable. Another example would includea blend of poly(lactic acid) and boric oxide.

Other degradable materials that undergo an irreversible degradation mayalso be suitable, if the products of the degradation do not undesirablyinterfere with either the conductivity of the permeable cement mass orwith the production of any of the fluids from the subterraneanformation.

In choosing the appropriate degradable material, one should consider thedegradation products that will result. These degradation products shouldnot adversely affect other operations or components. The choice ofdegradable material also can depend, at least in part, on the conditionsof the well, e.g., wellbore temperature. For instance, lactides havebeen found to be suitable for lower temperature wells, including thosewithin the range of 60° F. to 150° F., and polylactides have been foundto be suitable for well bore temperatures above this range. Also,poly(lactic acid) may be suitable for higher temperature wells.Dehydrated salts may also be suitable for higher temperature wells.

Also, we have found that a preferable result is achieved if thedegradable material degrades slowly over time as opposed toinstantaneously. Even more preferable results have been obtained whenthe degradable material does not begin to degrade until after thepermeable cement mass has developed some compressive strength. The slowdegradation of the degradable material helps, inter alia, to maintainthe stability of the permeable cement mass.

The specific features of the degradable material may be modified toprovide the permeable cement mass with optimum permeability whilemaintaining its desirable functionality. Preferably, the degradablematerial is selected to have a size, and shape to maintain substantialuniformity within the mixture. Whichever degradable material isutilized, the degradable materials may have any shape, depending on thedesired characteristics of the resultant voids in the mass including butnot limited to particles having the physical shape of platelets,shavings, flakes, ribbons, rods, strips, spheroids, toroids, pellets,tablets, or any other physical shape. The physical shape of thedegradable material should be chosen so as to enhance the desired shapeand relative composition of the resultant voids within the mass. Incertain preferred embodiments, a degradable material having a rod-likeparticle shape is used to create interconnecting channel-like voids inthe permeable cement mass. One of ordinary skill in the art with thebenefit of this disclosure will recognize the specific degradablematerial and the preferred size and shape for a given application.

The concentration of the degradable material in the permeable cementcomposition ranges from about 1% to about 70%, based on the weight ofthe cement in the composition. A concentration of degradable materialbetween about 20% and about 65% by weight of the cement in thecomposition is preferable. Additionally, the relative amounts of thedegradable material in the permeable cement composition should not besuch that when degraded, an undesirable percentage of voids result inthe permeable cement mass making the mass potentially ineffective inproviding a sand control means. One of ordinary skill in the art withthe benefit of this disclosure will recognize an optimum concentrationof degradable material that provides desirable values in terms ofenhanced permeability and sand control.

In an example of the methods of the present invention, a permeablecement composition of the present invention which forms a permeablecement mass in a subterranean formation to prevent the production ofsand with well fluids is prepared on the surface (either on-the-fly orby pre-blending it), and then pumped and/or displaced into thesubterranean formation and/or into perforations therein by way of a wellbore penetrating the formation. The methods of the present invention areparticularly suitable for preventing sand production in wells completedin unconsolidated formations wherein slotted liners, sand controlscreens, gravel packs, or the like have heretofore been utilized.

An embodiment of the methods of the present invention includes thefollowing steps. A permeable cement composition of the present inventionis provided that comprises a hydraulic cement, water, and a degradablematerial. The permeable cement composition is placed in the well bore inthe annulus adjacent to a sand control screen and a desired interval orzone in the subterranean formation. The permeable cement composition isallowed to set therein, whereby the composition fills and forms aconsolidated permeable cement mass in the annulus. As the permeablecement composition begins to gain compressive strength, the degradablematerial in the permeable cement composition is allowed to begin todegrade whereby a plurality of voids and channels are formed in thecement mass once it has set. After the permeable set cement mass hasbeen formed in the well bore, the well is produced and the permeablecement mass acts as, inter alia, a sand screen.

In another embodiment of the methods of the present invention, aperforated shroud is used rather than a sand screen. In this example ofthis method, the permeable cement composition of the present inventionis pumped into a desired area within the well bore, filling the annulusbetween the perforated shroud and the wellbore wall and the interior ofthe shroud, and then allowed to set. As the permeable cement compositionbegins to gain compressive strength, the degradable material in thepermeable cement composition is allowed to begin to degrade, whereby aplurality of voids and channels are formed in the cement mass when set.Once the cement has set, the set cement occupying the interior of theshroud is drilled out so that an annulus of the consolidated permeablecement mass remains in the well bore, inter alia, to prevent formationsands from being produced with desirable fluids.

In another exemplary embodiment, a temporary sealant can be used to sealoff the perforations in the perforated shroud before the shroud isplaced inside the wellbore. An embodiment of the cement compositionsdisclosed in the present invention can be placed in the annulus asconventionally applied as cement placement behind the casing, withoutdrilling or milling out the consolidated cement in the interior of theshroud. After the cement has been set, the temporary sealant sealing theperforations of the perforated shroud can be removed to restore thecommunication between the well bore interior and the reservoir. Thepermeable cement mass acts as, inter alia, a sand control means.

In certain preferred embodiments, the cement masses formed from thepermeable cement compositions of the present invention have apermeability of at least 1 darcies.

The permeable cement compositions of the present invention may be mixedon-the-fly or they may be pre-blended at the well site or thentransported to the wellsite. Thus, the present invention is well adaptedto carry out the objects and attain the ends and advantages mentioned aswell as those that are inherent therein. While numerous changes may bemade by those skilled in the art, such changes are encompassed withinthe spirit of this invention as defined by the appended claims.

1. A permeable cement composition for use in subterranean operationscomprising: a hydraulic cement; water, and a degradable materialselected from the group consisting of: (i) a degradable polymer selectedfrom the group consisting of polysaccharides, chitins, chitosans,proteins, aliphatic polyesters, poly(lactides), poly(glycolides),poly(ε-caprolactones), poly(hydroxybutyrates), polyanhydrides, aliphaticpolycarbonates, poly(orthoesters), poly(amino acids), poly(ethyleneoxides), and polyphosphazenes; and (ii) a dehydrated salt.
 2. Thecomposition of claim 1 wherein the permeable cement composition furthercomprises a dispersant.
 3. The composition of claim 1 wherein thehydraulic cement is selected from the group consisting of calcium,aluminum, silicon, oxygen, and sulfur.
 4. The composition of claim 1wherein the hydraulic cement is selected from the group consisting of aPortland cement, pozzolana cement, gypsum cement, high alumina contentcement, silica cement, high alkalinity cement, and low-density cement.5. The composition of claim 1 wherein the hydraulic cement is present inthe permeable cement composition in an amount ranging from about 50% toabout 60% by weight of the permeable cement composition.
 6. Thecomposition of claim 1 wherein the water is selected from the groupconsisting of fresh water, salt water, and brine.
 7. The composition ofclaim 1 wherein the water is present in an amount ranging from about 15%to about 40% by weight of the permeable cement composition.
 8. Thecomposition of claim 1 wherein the permeable cement composition furthercomprises a fluid loss additive.
 9. The composition of claim 1 whereinthe permeable cement composition is mixed on-the-fly.
 10. Thecomposition of claim 1 wherein the degradable polymer further comprisesa plasticizer.
 11. The composition of claim 1 wherein the degradablematerial comprises a stereoisomer of a poly(lactide).
 12. Thecomposition of claim 1 wherein the dehydrated salt is selected from thegroup consisting of anhydrous sodium tetraborate and anhydrous boricacid.
 13. The composition of claim 1 wherein the degradable material ispresent in an amount ranging from about 5% to about 70% by weight of thecomposition.
 14. The composition of claim 1 wherein the degradablematerial comprises particles having a rod-like shape.
 15. Thecomposition of claim 1 wherein the cement is a Portland cement andpresent in an amount of from about 30% to about 70% by weight of thepermeable cement composition; the water is fresh water and is present inan amount of from about 15% to about 40% by weight of the cementcomposition; and wherein the degradable material comprises a poly(lacticacid) particulate present in an amount of from about 5% to about 70% byweight of the permeable cement composition.
 16. A permeable cement massuseful in well bores penetrating a subterranean formation as a sandcontrol means having voids created by a degradation of a degradablematerial selected from the group consisting of: (i) a degradable polymerselected from the group consisting of polysaccharides, chitins,chitosans, proteins, aliphatic polyesters, poly(lactides),poly(glycolides), poly(ε-caprolactones), poly(hydroxybutyrates),polyanhydrides, aliphatic polycarbonates, poly(orthoesters), poly(aminoacids), poly(ethylene oxides), and polyphosphazenes; and (ii) adehydrated salt.
 17. The composition of claim 16 wherein the degradablepolymer further comprises a plasticizer.
 18. The composition of claim 16wherein the degradable material comprises a stereoisomer of apoly(lactide).
 19. The composition of claim 16 wherein the dehydratedsalt is selected from the group consisting of anhydrous sodiumtetraborate and anhydrous boric acid.
 20. The composition of claim 16wherein the degradable material is present in an amount ranging fromabout 5% to about 70% by weight of the composition.